Justification:
This species was described as separate from O. brevirostris only as recently as 2005. The available evidence supports the reasoning that there are fewer than 10,000 mature individuals and therefore the species meets the C criterion for Vulnerable in terms of population size. However, data are lacking to substantiate a continuing decline (C2). Similarly, no studies of population structure have been carried out so it is uncertain if either of the C2a subcriteria is met (i.e., whether no subpopulation is larger than 1000 mature, or all mature individuals are in a single subpopulation). Although the species could be listed as Data Deficient, Near Threatened is more appropriate given its limited range, low densities in surveyed areas, and its continuing vulnerability to bycatch. Rigorous, more extensive surveys are needed to support a reassessment of the species; it may then be found to qualify for listing as Vulnerable or possibly even Endangered.

Australian snubfin dolphins inhabit coastal, shallow waters of the tropical and subtropical zones of Australia, and possibly some parts of New Guinea (Beasley et al. 2005). In Australia, they occur from Broome, Western Australia, north and east to the Brisbane River, Queensland. The range along the northern Australian coast and New Guinea is poorly documented (Parra et al. 2002).

No overall population estimate is available for this species. There are only two abundance estimates for the Australian snubfin dolphin. Freeland and Bayliss (1989) roughly estimated that there were about 1,000 individuals in the Gulf of Carpentaria, Northern Territory, Australia. Their highest estimate was 1,227 individuals (CV=25%). However, the scientific credibility of that estimate has been challenged due to the difficulty of distinguishing Australian snubfin dolphins from other species during aerial surveys over turbid waters and later surveys conducted in the gulf that indicated a much lower population density (Parra et al. 2002; H. Marsh pers. comm). In Cleveland Bay, Queensland, abundance was estimated as < 100 (actual estimates ranged from 62-78, with CVs from 8-17%) (Parra 2005; Parra et al. 2006a). A survey conducted in May 2006 recorded only 15 groups totaling 88 animals distributed sparsely along portions of the northeastern part of the Kimberly coast (Debra Thiele pers. comm. to Brian Smith on 24 Jan 2007).

Although the species has been surveyed in only two areas (Cleveland Bay and Gulf of Carpentaria) which, together, comprise less than 20% of the species’ range, the results of those surveys, as well as the preliminary results from a reconnaissance survey of a portion of the Kimberly coast in 2006, indicate that the number of mature individuals is well below 10,000. It is assumed that the surveyed areas are broadly representative of the species’ density across its range. The population may be declining due to bycatch in commercial fishing nets (e.g. gillnets) and anti-shark nets.

Australian snubfin dolphins inhabit coastal, shallow waters and are most common in brackish estuaries. They have been seen in the same areas as Indo-Pacific humpback dolphins, which sometimes chase them aggressively. They occur most often near river and creek mouths, generally in waters less than 10 m deep (with a preference in some areas for very shallow waters, < 2 m deep) (Parra et al. 2006b)

Australian snubfin dolphins appear to be generalist feeders, taking a wide variety of fishes (including anchovies, sardines, eels, halibut, breams, grunters, and other estuarine species). They also eat cephalopods (squid, cuttlefish, and octopus), and crustaceans (shrimps and isopods, although the latter may be consumed incidentally).

The nearshore occurrence of this species makes it particularly vulnerable to human activities. However, most of its range in northern Australia and New Guinea has not been severely degraded. Substantial numbers of snubfin dolphins have been killed in anti-shark nets set to protect bathers (Paterson 1990). For example, in the Townsville region between 1968-1976, 15 of 24 dolphins known to have been killed were this species (Heinsohn 1979). The mortality rate of snubfin dolphins in anti-shark nets along the Queensland coast declined to an estimated 1.3/year between 1992-1995, coincident with the replacement of most anti-shark nets with baited drumlines (Gribble et al. 1998). In addition to the mortality in anti-shark nets, these dolphins die in inshore gillnets set across creeks, rivers and shallow estuaries primarily for barramundi (Lates calcarifer) and threadfin salmon (Polynemus sheridani) and (Eleutheronema tetradactylum) (Anderson 1995; Hale 1997).

Regulations, including net attendance rules and gear modifications, have been introduced to reduce bycatch but enforcement, especially in remote areas, has been inadequate (Hale 1997). Some protection is believed to accrue to snubfin dolphins from their presence in dugong protection areas (Parra et al. 2002).